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Complex numbers problem

  • 17-09-2011 06:48PM
    #1
    Registered Users, Registered Users 2 Posts: 20


    Sketch Argand Diagrams to represant the complex z = x+yi which satisfy the following conditions:

    |2z| = |z| + 6

    Thanks!


Comments

  • Registered Users, Registered Users 2 Posts: 5,657 ✭✭✭TheBody


    kelxx wrote: »
    Sketch Argand Diagrams to represant the complex z = x+yi which satisfy the following conditions:

    |2z| = |z| + 6

    Thanks!

    Well we can't give you the solution as it's against the charter so have you got any ideas? You are being asked to sketch on an argand diagram all the numbers that satisfy the equation. Might be helpful to do the following to get you started:

    We can rewrite |2z|=|z|+6 as 2|z|=|z|+6. Any idea what we could do next?


  • Registered Users, Registered Users 2 Posts: 20 kelxx


    that is the part im actually stuck with... i dont see how |2z| is the same as 2|z|

    |2z| = √ ((2x)^2 + (2y)^2)

    2|z| = 2√(x^2 + y^2)

    ?


  • Registered Users, Registered Users 2 Posts: 5,657 ✭✭✭TheBody


    kelxx wrote: »
    that is the part im actually stuck with... i dont see how |2z| is the same as 2|z|

    |2z| = √ ((2x)^2 + (2y)^2)

    2|z| = 2√(x^2 + y^2)

    ?

    Ah ok. I'll show you why that is true.

    [Latex]|2z|=| 2(x+yi)|[/Latex]
    [Latex]=|2x+2yi|[/Latex]
    [Latex]=\sqrt{(2x)^2+(2y)^2}[/Latex]
    [Latex]=\sqrt{4x^2+4y^2}[/Latex]
    [Latex]=\sqrt{4(x^2+y^2)}[/Latex]
    [Latex]=2\sqrt{x^2+y^2}[/Latex]
    [Latex]=2|z|[/Latex]

    Does that make sense?


  • Registered Users, Registered Users 2 Posts: 20 kelxx


    Ah yes i understand now! :) Thanks for the help!!


  • Registered Users, Registered Users 2 Posts: 5,657 ✭✭✭TheBody


    No problem. Glad I could help!!


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